Descartes' Error: Emotion, Reason, and the Human Brain is a book by neurologist Antonio R. Damasio, in which the author presents an argument that emotion and reason are not completely separate and, in fact, are quite dependent upon one another and essential to rational thinking.

This is a treatment of the controversial "mind/body" relationship, the issue of the mind/body relationship lying at the roots of psychology.

René Descartes, as a precursor to the modern study of psychology, gave us something to ponder about the mind/body relationship when he said: "I think, therefore I am." This saying is from the Discourse on Method, in which Descartes clarifies that he believes the mind and body to be independent entities, and that the mind can hypothetically exist without the body. Descartes' philosophy becomes the focus around which Damasio builds his counter-argument suggesting that the mind and body are not independent of each other, but very well integrated and dependent on each other. Damasio first argues that rationality stems from our emotions, and second, that our emotions stem from our bodily senses, completing his argument.